I would probably go by %. So for my 300RUM. YOu could go probably 4% over max and be safe. I know I went 4% and never saw pressure signs with RL25. All the way past recommended max with XLC.

But when I got down to loads in the 40-50gr region, I would be careful never to go over 2gr. Or if you do, go in .5 gr increments until you see pressure signs.